To investigate ¹⁸F-fluorodeoxyglucose (FDG) PET/CT imaging manifestations and digestive endoscopy of gastric mucosa-associated lymphoid tissue (MALT) lymphoma and evaluate whether maximum standardized uptake value (SUV_max) can reflect the tumor proliferation activity and diagnose the diffuse large B cell transformation.

¹⁸F-FDG PET/CT of 36 untreated histologically confirmed gastric MALT lymphoma patients (19 males, 17 females, age (46.4±18.1) years) between December 2012 and January 2019 in Nanjing Drum Tower Hospital were reviewed retrospectively. A positive or negative PET was defined based on visual analysis. ¹⁸F-FDG uptake above surrounding tissues in the regions of interest defined by the nuclear physician was considered positive, while negative was definited if the ¹⁸F-FDG uptake below surrounding tissues. Types of uptake included focal uptake and diffuse uptake. The characteristic findings of ¹⁸F-FDG PET/CT and digestive endoscopy (3 types: chronic gastritis-like type, depressed type and protruding type) in the consecutive patients were evaluated. The region of interest was drawn and the maximum standardized uptake value (SUV_max) was measured. One-way analysis of variance and the least siginficant difference t test were used to compare the SUV_max of 3 types of lesions and Mann-Whitney U test was used for comparison of SUV_max between lesions with/without diffuse large B cell transformation. The correlation between SUV_max and Ki-67 was assessed by Spearman rank correlation analysis. Receiver operating characteristic (ROC) curve analysis was performed to calculate the optimal cut-off value for the diagnosis of diffuse large B cell transformation.

Positive ¹⁸F-FDG PET/CT were found in 15 patients and the diagnostic accuracy was 41.7%(15/36). ¹⁸F-FDG uptake results were positive for all protruding tumors (5/5) mainly with focal uptake (4/5), but only 4/16 for chronic gastritis-like type tumors and 6/15 for depressed type tumors. SUV_max of protruding type tumors (10.7±6.4) was significantly higher than chronic gastritis-like type tumors (2.1±0.8) and depressed type tumors (2.7±1.4; F=13.010, all P<0.05). SUV_max (2.7(1.8, 5.0)) was associated with Ki-67 (10%(15%, 40%); r_s=0.345, P=0.039). SUV_max of tumors with diffuse large B cell transformation in 36 patients was significantly higher than that with no transformation (9.4(3.1, 14.8) vs 2.3(1.7, 3.9); z=-3.044, P=0.002), and the cut-off value of SUV_max was 6.5 (area under the curve: 0.788, P=0.011).

¹⁸F-FDG PET may be a useful method for evaluating protruding type gastric MALT lymphoma but not appropriate for chronic gastritis-like type or depressed type tumors. SUV_max may be a useful biomarker for tumor proliferation activity and can be used for diffuse large B cell transformation diagnosis in gastric MALT lymphoma patients.

Lymphoma, B-cell, marginal zone; Stomach; Positron-emission tomography; Tomography, X-ray computed; Deoxyglucose; Endoscopy, gastrointestinal